Problem: $(12)-(23+13i)=$ Express your answer in the form $(a+bi)$.
Answer: Background Complex numbers can be added or subtracted by separately adding or subtracting their real and imaginary terms. To add or subtract complex numbers: Expand parentheses (attending to minus signs outside of parentheses if necessary) Combine all real terms (terms that do not contain $i$ ), and add or subtract them. Combine all imaginary terms (terms that contain $i$ ), and add or subtract them. Combining Like Terms $\begin{aligned} ({12})-({23}+{13}i)&={12}-{23}-{13}i \\\\ &={-11}{-13}i \end{aligned}$ Summary $({12})-({23}+{13}i)={-11}{-13}i$